From ANIMAL PEOPLE, March 2009:

Horse racing evolved as “The Sport of Kings,” since kings
were among the first people who could afford to breed and race highly
valued animals kept by others mostly for work.
Animal fighting, regardless of any terms applied to the
human participants, by contrast evolved as “The Sport of Trash.”
The plastic garbage bags full of “sexed” male chickens
awaiting live maceration at any hatchery serving the egg industry
illustrate why. Cockfighting, bullfighting, and dogfighting each
originated through the quest to find profitable uses for lives that
would otherwise be snuffed out and discarded: birds who would never
lay eggs, cattle who would never give milk, and barge-born mongrel
pups who might combine big-dog stamina with small-dog feistiness,
but would grow up to be too small to pull carts, too big to hunt rats.
Gambling money and the evolution of paying audiences for
animal fighting eventually separated the lineage of most gamecocks,
fighting bulls, and fighting dogs from their barnyard and waterfront
ancestors, but not entirely. The public participatory forms of
bullfighting practiced in India as jallikattu and dhirio, for
example, and the Brazilian version called farra du boi, are little
changed from ancient origins.
Surplus bull calves in early agrarian societies might be
castrated and trained to draw plows and carts, but relatively few
were needed for work. Bull calves might also be raised as steers,
for beef; but until the advent of mechanized grain production, few
people could afford to keep and fatten cattle just to be eaten.
Yet many tried. Around the world, agrarian societies
typically tried to feed most of their young and healthy animals
through the winter, then culled them at midwinter solstice and
spring equinox festivals. The killing was sometimes ritualized as
sacrifice, sometimes as sport and entertainment, and often as all
three.

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